Mixing bowl for a planetary centrifugal mixer, and mixer receiving such bowls

ABSTRACT

The planetary centrifugal mixer comprises a fixed axis (4) on which is rotatably mounted an arm (10) carrying a fixed rod (11) extending upwardly. The arm (10) is rotated about the axis (4) by means of a drive pinion (9), and at the same time a mixing bowl (22) fitted on the rod (11) is rotated about the rod, the drive pinion (16) of the bowl (22) being coupled by an intermediate pinion (18) to a pinion (19) integral with the fixed axis (4). The side wall (24) of the bowl (22) has at least two segments (28), the curvature radius being greater than that of the remaining segments (27). A central guide (29) projects from the bottom (23) of the bowl (22), its outer shape being matched to the shape of the lateral wall (24).

The present invention relates to a mixing bowl for planetary centrifugalmixers, and to a planetary centrifugal mixer receiving such bowls.

Planetary centrifugal mixers are known, for example through PatentApplication DE-A-2,209,850 and Patent Application EP-A-207,335, intendedfor example for the preparation of mixtures used in dentistry,particularly alginate-based pastes for taking dental impressions andcomprising at least one arm mounted movable in rotation about a verticalaxis, means provided on the said arm so as to permit the mounting of abowl movable in rotation about an axis sloping with respect to the axisof rotation of the arm, and driving and planetary transmission means forsimultaneously causing the arm to turn about its vertical axis ofrotation and the bowl about its axis of rotation sloping with respect tothe vertical. The bowls provided on these known mixers are bowls ofrevolution comprising a bottom and a peripheral lateral wall ofcylindrical general shape. However, the mixing effect to which theproducts to be mixed are subjected in such bowls often proves not to beoptimal, in view, among other things, of the consistency of the productsto be mixed and of the effect of adherence of these products to thebowls.

In order to improve this mixing effect, it has already been proposedthrough Patent Application DE-A-2,001,301 to give such mixing bowls aninternal shape which is not of revolution. According to FIGS. 17 and 18of this document, the internal space of a mixing bowl of cylindricalexternal configuration has the shape of a transverse slit defined by twoparallel flat walls and by two semi-circular end walls.

Such a bowl proves not to give satisfaction because an excessiveunbalance is produced, when the bowl rotates, owing to the shape of thelatter and to the irregular movement which the products to be mixedundergo in the bowl.

Moreover, another disadvantage of the known mixing bowls consists in thedifficulties in extracting the mixed product from the bowl. Thisextraction is generally effected with the aid of a spatula which it isnecessary to pass several times into the bowl so as to remove therefromthe whole of the contents.

Furthermore, the known bowls, when they are light, that is to say with athin peripheral lateral wall, undergo during mixing deformations underthe effect of the centrifugal force.

Another problem relating to the known bowls concerns the closure ofthese bowls with the aid of a detachable lid fitted onto or into thebowl. If this closure is hermetic, in order to protect the contents ofthe bowl from the ambient air, a partial vacuum (suction cup effect) isproduced inside the bowl when the lid is removed. In order to remedythis suction cup effect, it has already been proposed to pierce a smallhole in the lid, but in this case the bowl and its lid do not constitutea hermetic enclosure and, moreover, when the lid is removed, an airintake is produced through the hole, inducing a jet of air whichresults, when the products contained in the bowl are in powder form, ina portion of these products being blown out of the bowl at the momentwhen the lid is removed.

In a general way, the known centrifugal planetary mixers of the typedefined above have moreover the disadvantage of a high cost owing to thecomplicated structure of the mixer as a whole and in particular of themeans for supporting the rotary arm and of the means for supporting themixing bowl on the rotary arm. In fact, these support means generallycomprise a rotary shaft for the arm as well as a rotary shaft for abowl-carrier, which involves the use of bearings (rolling bearings) formounting these shafts. Moreover, the holding of the bowls on thesemixers is often unsatisfactory.

The present invention has as its subject a mixing bowl for a planetarycentrifugal mixer, this bowl ensuring an effective mixing whilefacilitating the removal of the mixed products from the bowl. Theinvention also has as its subject a mixing bowl with lid, preventing anydeformation of the bowl during mixing and permitting both a hermeticclosure of the bowl by the lid and a removal of the lid without partialvacuum effect and without air intake capable of causing, in the case ofpowdery products to be mixed, these products to be blown out of thebowl. The invention further has as its subject a mixing bowl and aplanetary centrifugal mixer which are designed so that the bowl isperfectly held in position on the mixer. The invention moreover has asits subject a planetary centrifugal mixer of simpler, therefore morereliable and less costly, structure than the known mixers.

The mixing bowl according to the invention for a planetary centrifugalmixer comprises a bottom and a peripheral lateral wall of cylindricalgeneral shape. According to the invention, the lateral wall has, atleast internally, at least over the lower part of its height, in zonesspaced regularly and distributed over the periphery of the bowl, atleast two curved segments the radius of curvature of which is greaterthan the radius of curvature of the remaining zones. Moreover, the bowlcomprises a central guide projecting upwards on the bottom and having anon-cylindrical external shape such that the radial distance between theinternal surface of the peripheral lateral wall and the said guide issubstantially the same over the entire periphery of the guide.

In the context of the invention, the said segments of the peripherallateral wall of the bowl, the radius of curvature of which is greaterthan the radius of curvature of the remaining zones, may be two, three,or even four in number. The higher this number, the lower must be thespeed of rotation of the bowl. However, the higher the number of thesesegments, the less these segments are pronounced and therefore the lesseffective they are.

The mixing bowl according to the invention may be fitted with a fittinglid pierced with a central hole in its head. In this case, the said lidhas a depth of fitting onto or into the bowl which is greater than thethickness of its head and the central guide of the bowl projects upwardson the bottom of the bowl over such a height that it closes the hole ofthe lid solely when the latter is fitted home onto or into the bowl.

Thus, the central guide interacts with the hole of the lid so as toprevent any deformation of the bowl under the effect of the centrifugalforce and so as to ensure a hermetic closure of the bowl when the lid isfitted home onto or into the latter. When the lid is removed, thecentral guide clears the hole of the lid before the latter is completelytaken off, which permits a balancing of the internal pressure of thebowl before the complete removal of the lid. Thus, neither partialvacuum inside the bowl, nor an air intake capable of flowing out thepowdery products to be mixed contained in the bowl, are produced.

In order to improve the holding of the bowl on the rotary arm of themixer, the central guide of the bowl has a bore opening on the side ofthe bottom of the bowl, which allows the bowl to be fitted onto arod-shaped holding member mounted on the arm. The bowl is thus held atits center, over all or part of its height, which excludes any risk ofejection of the bowl during operation, for example because of adefective fitting of the bowl onto the arm.

The planetary centrifugal mixer according to the invention intended toreceive at least one bowl of the type defined above comprises at leastone arm mounted movable in rotation about a vertical axis. Means areprovided on the said arm for mounting the bowl movably in rotation aboutan axis sloping with respect to the vertical. Driving and planetarytransmission means are provided moreover so as to cause the said arm andthe said bowl to turn simultaneously about their respective axes ofrotation. According to the invention, the means for mounting the bowl onthe arm consist of a rod of circular cross-section attached rigidly tothe arm, this rod being adapted to interact with the bore of the centralguide of the bowl when the latter is fitted onto the said rod.

This rod, the rigid attachment of which onto the arm is very simple,ensures a much better holding of the bowl than the bowl-carriers of theknown mixers which must be deep so that the bowl can be fitted thereonand, at the same time, be held and driven in rotation. The driving ofthe bowl in rotation on the mixer according to the invention can beperformed directly by a pinion mounted coaxially with the rod inrotation on the top of the arm and presenting on its upper surface meanscapable of interacting, with a view to the driving, with the bottom ofthe bowl.

Preferably, the arm of the mixer according to the invention is mountedin rotation on a fixed spindle and bears on the lower side a pinion forits driving in rotation. The planetary transmission means for drivingthe bowl in rotation about its axis comprise a pinion integral with thefixed spindle of the arm, on the upper side of the arm, this pinionbeing coupled by an intermediate pinion mounted in rotation on the armwith the said pinion coaxial with the said rod.

Preferably, the said pinion coaxial with the rod has, on top, meanshaving a shape complementary to the non-circular external shape of thebowl.

With reference to the accompanying diagrammatic drawings, one embodimentof a planetary mixer according to the invention, and two embodiments ofbowls for such a mixer will be described below in greater detail; in thedrawings:

FIG. 1 is an axial cross-section of a mixer according to the inventionwith two bowls;

FIGS. 2 and 3 are plan views of two variant bowls without the lids.

According to FIG. 1, a centrifugal planetary mixer, only the movingparts of which are shown, comprises a double arm 1, rotatably mounted by2 rolling bearings 2 and 3 on a vertical spindle 4 attached to a support5 with the aid of a nut 6 screwed onto the threaded lower end 7 of thespindle 4, passing through a hole of the support 5. The double arm 1bears, on the lower side, a pinion 8 concentric with the spindle 4, thispinion 8 being operated by a pinion 9 driven by a motor which is notshown.

The double arm 1 comprises two arms 10 disposed in a same containingplane through the spindle 4. Each arm 10 bears, in the vicinity of itsfree end, a rod 11 rigidly attached to the arm 10. Each rod 11 comprisesan attachment part 12 passing through the arm 10 and rendered integralwith the latter by a nut 13, and a cylindrical mounting part 14projecting upwardly beyond the arm 10 and terminated by a conical tip15.

It should be noted that the axis of the rod 11 is sloping with respectto the vertical, that is to say with respect to the spindle 4, by anangle of between about 40° and 60°.

A pinion 16 is rotatably mounted by a rolling bearing 17 on the rod 11on the upper side of each arm 10. This pinion meshes with anintermediate pinion 18 which is rotatably mounted on the arm 10 andwhich itself meshes with a pinion 19 integral with the upper end of thespindle 4. In the example shown, the spindle 4 and the intermediatepinions 18 are capped by a cover 20 secured by screws 21.

Each rod 11 serves to receive a mixing bowl 22 shown in FIG. 2 in planview and in FIG. 1 in axial cross-section along line I--I of FIG. 2.

The bowl 22 comprises a substantially flat bottom 23 and a peripherallateral wall 24 which has a cylindrical shape in its upper part 25 and anoncylindrical shape in its lower part 26. As is particularly apparentin FIG. 2, the lower part 26 of the lateral wall 24 comprises twoopposing segments 27 having the same radius of curvature as the upperpart 25 of the lateral wall 24, and two opposing segments 28 which,offset respectively by 90° with respect to the segments 27, have agreater radius of curvature than the segments 27.

Each bowl 22 comprises moreover a central guide 29 projecting upwards onthe bottom 23 and having such an external shape that the radial distancebetween the internal surface of the lower part 26 of the peripherallateral wall 24 and the said guide 29 is substantially the same over theentire periphery.

As is apparent in FIG. 1, the guide 29 retains this external shape overthe entire height of the lower part 26 of the lateral wall 24 and isthen extended upwards by a part 31 tapering progressively in the shapeof a truncated cone about as far as the upper edge of the bowl 22. Thepart 31 is followed upwards by a cylindrical part 32 which is terminatedby a conical tip 33.

A lid 34 fitted into the aperture of the bowl 22 has at its center ahole 35 the diameter of which is substantially equal to the diameter ofthe cylindrical part 32 of the guide 29. The thickness (of the head) ofthe lid 34 is less than the fitting depth of the lid 34.

The guide 29 has internally a bore 36 which opens on the side of thebottom 23 and the shape of which is adapted to the shape and to thediameter of the part 14 of the rod 11.

It should further be noted that the pinion 16 rotatably mounted on therod 11 itself integral with the arm 10 comprises, on the side turnedtowards the bowl 22, a projecting part 37 shaped in accordance with the(noncircular) external shape which the bowl 22 has in its lower part, sothat when the bowl 22 is fitted onto the part 14 of the rod 11, thelower part of the bowl 22 comes to fit into the part 37 of the pinion16, the bowl 22 then being integral in rotation with the pinion 16.

It should further be noted that the cylindrical part 32 of the guide 29has such a height that it closes the hole 35 of the lid 34 only when thelatter is fitted home into the bowl 22. Consequently, the guide 29clears the hole 35 of the lid 34, thus permitting a balancing ofpressure between the inside of the bowl and the outside, as early as thebeginning of the movement of removal of the lid 34 from the bowl 22.This therefore eliminates any partial vacuum effect opposing the removalof the lid. Moreover, because of the relatively large diameter of thehole 35, this prevents, when the lid is removed, the creation of a jetof air towards the inside of the bowl 22, and thus prevents the productscontained in the bowl 22 from being blown out when the said products arein powder form.

In connection with this, it should be noted that the mixer according tothe invention may find applications in all fields, but that one of itsparticularly advantageous applications is found in the field ofdentistry, with a view to the preparation of paste, particularlyalginate-based paste, for taking impressions. The use of the bowlsaccording to the invention makes it possible to prepare in advance andto conserve in the bowls according to the invention predeterminedquantities of alginate powder, the leaktight closure of these bowlspreventing the alginate from being spoiled through exposure to the air.Then, for each preparation of a quantity of paste for takingimpressions, it is sufficient to select the bowl containing the requiredquantity, to open this bowl, to add thereto a corresponding quantity ofwater and then to proceed to mix the paste on the mixer.

The presence on the mixer according to the invention of two arms 10 eachbearing a rod 11 makes it possible to prepare simultaneously in twobowls, either a double dose of a mixture, or two different mixtures, forexample of different viscosities. In the case of use of a single bowl onone arm, it is sufficient to place a balancing washer on the rod 11 ofthe other arm.

The bowls according to the invention make it possible in this case touse normal alginate instead of the "dust free" type alginate which mustnecessarily be used with the known mixing bowls in order to prevent orreduce the risks of alginate in powder form being blown out when thebowls are opened, as a result of the jet of air which is then producedbecause of the small-sized hole, hitherto provided in the lids of mixingbowls.

The mixing bowl 22a according to FIG. 3 differs from the mixing bowl 22of FIG. 2 by the shape of the lower part 26a of the lateral wall 24a andby the external shape of the central guide 29a. In fact, according toFIG. 3, the part 26a of the lateral wall 24a comprises three segments27a having the same radius of curvature as the upper part 25a of thelateral wall 24a, and three segments 28a having a greater radius ofcurvature, the three segments 27a and the three segments 28a beingoffset respectively by 120°. Here also, the central guide 29a has, inits lower part 30a, such an external shape that the distance separatingthe part 30a of the central guide 29a from the internal surface of thepart of lateral wall 24a is substantially the same over the entireperiphery, this facilitating the removal of the substances mixed in thebowl with the aid of a spatula having a width substantiallycorresponding to the said distance.

Another advantage of the guide 29, 29a of the bowl and of the lid 24interacting with this guide consists in the rigidity which this givesthe bowl, that is to say in the absence of deformation of the bowlduring the mixing under the effect of the centrifugal force. In fact,the lid thus always ensures the centring of the peripheral lateral wallon the guide itself centred on the rod 11 of the mixer.

I claim:
 1. A mixing bowl for a planetary centrifugal mixer,comprising:a bottom; a lateral wall extending from peripheral portionsof the bottom and having an overall shape which is substantiallycylindrical and an inner surface which, along at least lower portions ofthe lateral wall, includes a plurality of regularly spaced zones whereintwo of the regularly spaced zones have a first radius of curvature andare separated by another two of the regularly spaced zones having asecond radius of curvature greater than the first radius of curvature;and a central guide extending from central portions of the bottom andincluding an outer surface having a shape wherein radial distancesbetween the inner surface of the lateral wall and the outer surface ofthe central guide are substantially the same.
 2. The mixing bowl ofclaim 1 wherein the regularly spaced zones include three of theregularly spaced zones with the first curvature separated by three ofthe regularly spaced zones with the second curvature.
 3. The mixing bowlof claim 1 which further includes a lid for engaging the lateral wall,for enclosing the mixing bowl, wherein the lid includes a centrallydisposed aperture for engaging a tip extending from the central guide ofthe mixing bowl.
 4. The mixing bowl of claim 3 wherein the central guidehas a height above the bottom such that the aperture of the lid isenclosed by the tip of the central guide when the lid is received by thelateral wall of the mixing bowl.
 5. The mixing bowl of claim 4 whereinthe central guide terminates in a conical end portion including the tipof the central guide.
 6. The mixing bowl of claim 5 wherein the tip iscylindrical, for engaging a round aperture of the lid.
 7. The mixingbowl of claim 5 wherein the central guide includes a bore extending tothe bottom of the mixing bowl.
 8. The mixing bowl of claim 7 wherein thebore is cylindrical.
 9. A planetary centrifugal mixer for receiving amixing bowl;wherein the mixing bowl comprises a bottom, a lateral wallextending from peripheral portions of the bottom and having an overallshape which is substantially cylindrical and an inner surface which,along at least lower portions of the lateral wall, includes a pluralityof regularly spaced zones wherein two of the regularly spaced zones havea first radius of curvature and are separated by another two of theregularly spaced zones having a second radius of curvature greater thanthe first radius of curvature, and a central guide extending fromcentral portions of the bottom and including an outer surface having ashape wherein radial distances between the inner surface of the lateralwall and the outer surface of the central guide are substantially thesame; and wherein the centrifugal mixer comprises an arm mounted forrotation about a substantially vertical axis, a rod connected to andextending from the arm and having a substantially circularcross-section, for receiving the central guide of the mixing bowl,wherein the central guide includes a bore for engaging the rod so thatthe mixing bowl is rotatable about an axis defined by the rod anddisposed at an angle to the vertical axis of the arm, and planetarytransmission means including driving means for causing the arm to rotateabout the vertical axis while simultaneously causing the mixing bowl torotate about the axis defined by the rod.
 10. The planetary centrifugalmixer of claim 9 wherein the arm is received by a fixed verticalspindle, for rotation about the spindle, and includes a pinion forrotating the arm.
 11. The planetary centrifugal mixer of claim 10wherein the arm further includes a pinion for rotating the mixing bowl,wherein the pinion for rotating the mixing bowl is pivotally associatedwith the rod extending from the arm.
 12. The planetary centrifugal mixerof claim 11 wherein a fixed pinion is associated with the spindle forreceiving the arm, and engages an intermediate pinion pivotallyassociated with the arm and engaging the pinion for rotating the mixingbowl.
 13. The planetary centrifugal mixer of claim 9 which includes twoarms for simultaneously receiving two mixing bowls.